Treatment of paper composed of partially acylated cellulose fibers



OPACITY Oct. 9, 1962 c. J. MALM ETAL 3,057,755

TREATMENT OF PAPER COMPOSED OF PARTIALLY ACYLATED CELLULOSE FIBERS Filed Jan. 12, 1959 csr NE+ CEL ULOSE 95% 011 0/ A 0 I Ac'TATE 87 5% CH3 OH 0.5% CELLULOSE ACETFITE 86 85 84 OPACITY UNmEATED 83 PA PAPER T1 0 BASED ON PAPER Carl JMalm Gerald G. Gandy INVENTORS United States Patent Ofifice 3,057,755 Patented Oct. 9, 1962 This invention relates to a method for improving the opacity of solvent treated paper made from partially acetylated cellulose fibers by incorporating titanium dioxide in the treating composition.

A simplified flow diagram illustrating treating paper composed of partially acylated cellulose fibers in accordance with the invention is as follows:

Paper of partially acylated cellulose fibers Dipped in composition of TiO in organic liquid having a swelling eiiect Excess solution removed Solvent evaporated from the sheet Paper sheet calendered According to the Institute of Paper Chemistry, about 4060% of the strength of a Waterleaf paper sheet is contributed by the fiber strength, the balance being contributed by fiber-to-fiber binding. The making of a paper, the fibers of which have an acetyl content within the range of 1525%, has been suggested. This paper exhibits considerable dimensional stability improvement over paper prepared from conventional wood pulp. The effect of moisture on paper prepared from wood pulp has been recognized and to overcome this effect various sizing materials have been incorporated therewith. However, by partially acetylating the cellulose fibers in making paper, it has been found that these sizing additives can be dispensed with yet resistance to the eflfect of moisture is obtained.

Cellulose fibers, upon acetylation, lose some of their strength and, hence, the paper prepared therefrom does not exhibit a tear strength as high as that of a paper prepared from the same cellulose fibers not reacted upon by a chemical reagent. To improve the wet strength, fold characteristics, and Mullen value of paper sheets composed of partially acetylated cellulose fibers, procedures have been developed and are claimed in U.S. Patent No. 2,992,156, issued July 11, 1961, to Oliver J. Schulwitz, filed March 3, 1958, which involves wetting the paper with an organic liquid which exerts a swelling action on cellulose acetate, such as acetone, methylene chloride, methylene chloride-methanol, or the like, which liquid may or may not contain cellulose ester in solution therein. After the paper has been so treated, it is dried. By this treatment the opacity of paper prepared from partially acetylated fibers is appreciably reduced.

Another procedure which has been developed for improving the wet strength, Mullen value and fold characteristics of partially acetylated fiber paper is that described and claimed in U.S. application Ser. No. 786,043 of Malm, Herdle and Gandy, filed of even date, which includes treatment with an aliphatic alcohol solution of a cellulose ester and a plasticizer following which the paper is subjected to heat and pressure to give a smooth finish stable to water wetting and redrying. The treatment of paper as there described may result in appreciable loss of opacity.

One object of our invention is to provide a procedure for the treatment of partially acetylated cellulose fiber paper in which the opacity of that paper is retained although it has been treated to impart good strength characteristics thereto. Other objects of our invention will appear herein.

In its broadest aspects our invention comprises incorporating titanium dioxide in the solvent solution which is employed for treating partially acetylated fiber paper to retain its opacity characteristics. The amount of titanium dioxide employed is such that the paper retains at least 4% of titanium dioxide based on the weight of the paper. As the titanium dioxide is not considered to be selectively sorbed by the paper, the amount of that material added to the solvent solution with which the paper is treated is determined by the amount of solvent solution retained by the treated paper. This procedure has a decided advantage over the procedures heretofore used in applying titanium dioxide in water suspension to paper in that from the water suspension systems only a fraction of the titanium dioxide has been taken up by the paper and there has been a tendency for the titanium dioxide to form clumps. By the treatment using the solvent material as the suspending agent for the titanium dioxide, the titanium dioxide has remained in suspension and has given a uniform opacity to the paper. It is preferable in operating in accordance with our invention to employ the titanium dioxide in finely divided condition, such as of l to 20 microns diameter.

Our invention involves the addition of titanium dioxide to a solvent solution such as is employed in accordance with the procedure of U.S. Patent No. 2,992,- 156 of Oliver J. Schulwitz or to an alcohol solution of a cellulose ester and plasticizer such as described in the Malm, Herdle and Gandy application, filed of even date. It is desirable that the titanium dioxide be used in an amount at least 1.7% by weight of the amount of solvent which is employed, and it is even more desirable if the titanium dioxide be used in an amount such as 2.5% up to 10% by weight of the amount of solvent. The amount used depends upon the solvent system which determines the amount of liquid retained by the paper.

The accompanying drawing illustrates the effect of the solvent treatment of partially acetylated cellulose fiber paper when no titanium dioxide or only limited quantities of titanium dioxide are used compared with the use of a substantial quantity of T10 in accordance with the invention. It may be seen therefrom that whereas the opacity of the untreated paper is in the vicinity of 84 the treatment with solvent reduces that opacity to a point less than 80, and it is only when the paper picks up at least 4% of titanium dioxide that the opacity of that paper is comparable to that of the untreated paper. With increased pick-up of titanium dioxide the opacity of the paper substantially increases so that it becomes superior to that of the paper which had not been treated. In the compositions in accordance with our invention, it is ordinarily desirable that some cellulose ester be present therein, such as in a proportion of at least 0.5% up to 25%, the cellulose ester aiding in the bonding of the cellulose fibers and in promoting the adherence of the titanium dioxide to those fibers. The following examples illustrate our invention:

Example] Titanium dioxide which had been finely divided by milling in a suitable machine was mixed with an acetone solution of cellulose acetate in the proportion of 4.9 parts of titanium dioxide, 0.9 part of cellulose acetate and 94.2 parts ofacetone. Paper which had been prepared from wood pulp fiber that had been acetylated to an acetyl content of 22% and which had a base weight of 20 lbs. per 1000 sq. ft. was dipped in a bath having the composition described in sufiicient amount to saturate the paper. The excess solution was removed with squeeze rolls and solvent was evaporated from the sheet, which was then supercalendered using 4 nips at 140 F. A sheet of an opacity greater than that of the opacity of the original partially acetylated fiber paper sheet was obtained.

ExampleZ Titanium dioxide which had been finely divided by milling in a suitable machine was mixed with a solution of cellulose acetate butyrate and dibutyl phthalate in isobutyl alcohol in the following proportions:

Percent Titanium dioxide 5 Dibutyl phthalate 5 Cellulose acetate butyrate (approximately 38% butyryl) 5 Isobutyl alcohol 85 Paper which had been prepared from wood pulp fibers that had been acetylated to an acetyl content of approximately 22% and which had a base weight of 19.5 lbs. per 100 sq. ft. was dipped into the solution of cellulose acetate butyrate and dibutyl phthalate in alcohol which contained titanium dioxide in suspension at 60 C. The paper was run through squeeze rolls which removed the excess solution from the sheet leaving less than 1 part of solution per part of paper. The alcohol was evaporated from the sheet which was then supercalendered using 4 nips at a temperature of 140 F. The opacity of the paper thus obtained was 87 as compared with an opacity value of 82 for paper which had been similarly treated Without the use of titanium dioxide.

We claim:

1. In the treating of paper prepared from partially acylated fibers wherein its fibers are impregnated with a composition comprising an organic liquid which has at least a cellulose ester swelling effect, followed by drying to improve the physical properties thereof, the step which comprises adding to the composition prior to that treatment titanium dioxide of l micron size in the amount of 17-10% of the organic liquid employed whereby the paper retains at least 4% of titanium dioxide.

2. In the treatment of paper composed of partially acetylated fibers of 15-25% acetyl content wherein those fibers are impregnated with a composition comprising an organic liquid which has at least a cellulose ester swelling effect followed by drying, to improve the physical properties of that paper, the step which comprises adding to the composition titanium dioxide of 1-20 micron size in the amount of 17-10% of the organic liquid employed whereby the paper retains at least 4% of titanium dioxide.

3. In the treating of paper prepared from partially acetylated fibers of 15-25% acetyl content wherein those fibers are impregnated with a composition comprising an organic liquid containing 0.525% of a cellulose derivative which organic liquid has at least a cellulose ester swelling effect, followed by drying the paper to improve its physical properties, the step which comprises adding to the composition titanium dioxide of 1-20 micron size in an amount of 17-10% of the organic liquid whereby the paper retains at least 4% of titanium dioxide.

4. A method of treating partially acylated fiber paper which comprises wetting the paper with a solution of a cellulose ester in an organic liquid having at least a swelling effect on cellulose ester which solution contains 1.7- 10% of titanium dioxide of l-20 micron size, followed by removing excess liquid and drying the paper whereby at least 4% of titanium dioxide is retained, the physical properties of the paper is improved and its opacity is maintained.

5. A method of treating partially acetylated fiber paper which comprises impregnating the paper with a solution of cellulose ester and a plasticizer therefor in alcohol which solution contains 17-10%, based on the alcohol, of titanium dioxide of 120 micron size, removing excess liquid and drying the paper so as to leave at least 4% titanium dioxide therein whereby the paper is improved in physical properties and its opacity is maintained.

6. A method of treating paper prepared form par tially acetylated fibers which comprises wetting the paper with an organic liquid which exerts a swelling action on cellulose acetate and subsequently removing excess liquid and drying the paper in a manner to leave at least 4% of titanium dioxide therein whereby the physical properties of the paper are improved and its opacity is maintained.

7. A method of treating paper prepared from wood pulp fibers having an acetyl content of 22% which comprises dipping the paper in a bath composed of 4.0 parts of titanium dioxide, 0.9 part of cellulose acetate and 94.2 parts of acetone and subsequently removing excess liquid and drying the paper in a manner to leave at least 4% of titanium dioxide therein whereby the physical properties of the paper are improved and its opacity is maintained.

8. A method of treating paper prepared from wood pulp fibers having an acetyl content of approximately 22% which comprises dipping the paper into a solution composed of 5% of titanium dioxide, 5% of dibutyl phthalate, 5% of cellulose acetate butyrate and isobutyl alcohol, subsequently passing the paper through squeeze rolls to reduce the solution therein to less than 1 part per part of paper and drying whereby the physical properties of the paper are improved and its opacity is maintained.

References Cited in the file of this patent UNITED STATES PATENTS 2,035,504 Parkinson et al Mar. 31, 1936 2,095,028 Claik Oct. 5, 1937 2,186,957 Collings et a1. Jan. 16, 1940 2,287,348 Hayden June 23, 1942 2,351,174 Whitehead June 13, 1944 2,357,962 Leemann et al Sept. 12, 1944 2,814,617 Hagenbuch et a1 Nov. 26, 1957 2,955,958 Brown Oct. 11, 1960 

1. IN THE TREATING OF PAPER PREPARED FROM PARTIALLY ACYLATED FIBERS WHEREIN ITS FIBERS ARE IMPREGNATED WITH A COMPOSITION COMPRISING AN ORGANIC LIQUID WHICH HAS AT LEAST A CELLULOSE ESTER SWELLING EFFECT, FOLLOWED BY DRYING TO IMPROVE THE PHYSICAL PROPERTIES THEREOF, THE STEP WHICH COMPRISES ADDING TO THE COMPOSITION PRIOR TO THAT TREATMENT TITANIUM DIOXIDE OF 1-20 MICRON SIZE IN THE AMOUNT OF 1.7-10% OF THE ORGANIC LIQUID EMPLOYED WHEREBY THE PAPER RETAINS AT LEAST 4% OF TITANIUM DIOXIDE. 